Turbidity measurements of bacterial cultures in some available commercial instruments☆

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the emerging opportunistic pathogens that can cause food poisoning and is responsible for several infectious diseases, including hospital-acquired infections. The main objective of this work was to assay the antibacterial effect of Origanum grosii essential oil (OGEO) and NaCl, alone and in combination against the MRSA growth. For this purpose, response surface methodology (RSM) was adopted to generate a mathematical model representing this effect. O. grosii was harvested from the north of Morocco. GC-FID and GC/MS techniques were used in order to determine the chemical profile of OGEO. The main compounds of OGEO were carvacrol (49.29%), thymol (13.12%), p-cymene (12.68%), and γ-terpinene (8.78%). The method of micro-dilution was used in order to determine the minimal inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC). The MIC value of OGEO was 0.5% (v/v), while the MBC value was equal to 1%(v/v). The OGEO showed a strong bactericidal effect against MRSA. RSM applied at two different incubation times, 6 h and 11 h, and at the total time average value (TAV), allowed to create a mathematical model representing the kinetics of MRSA growth depending to the concentrations of OGEO and salt. The interaction between these two variables was significant. The quadratic polynomial regression was sufficient to adequately represents the observed results with a high coefficient of determination R² ranging from 95.8 to 96.4%. A synergy at first order was observed between the two factors, but it was not present at all time points; a slight antagonistic effect was observed at time t = 6 h. These results show that RSM provided a useful and accurate mathematical method by combining low sub-inhibitory concentrations of OGEO with NaCl that can be used as a natural product against MRSA infections or as an additive in the food system.

Ensuring the effective antibacterial with enhanced cytocompatibility of zinc oxide (ZnO) nanomaterials is still a challenging task. Here, we initially coated ZnO NPs with polydopamine (PDA), then integrated hydroxyapatite (HAp), and eventually obtained HAp@ZnO/PDA composite NPs to investigate the cytocompatible and antibacterial properties of the NPs in terms of different concentrations (200 to 6.25 µg/mL). The morphological analysis confirmed that the PDA-coating assisted the facile integration of HAp on the surface of ZnO/PDA NPs, and successfully synthesized the HAp@ZnO/PDA-06, HAp@ZnO/PDA-12, and HAp@ZnO/PDA-24 NPs by varying the modified-simulated body fluid (m-SBF) incubation time. Moreover, the morphological analysis also acknowledged that the prolonged incubation period (i.e., more than 6 h) is not recommendable for better HAp integration. Similarly, the antibacterial test confirmed that all three types of HAp@ZnO/PDA composite NPs including pure ZnO and ZnO/PDA NPs exhibited dose-dependent bactericidal action, and they were more efficient against Gram-positive Staphylococcus aureus compared to Gram-negative Escherichia coli. According to the results, the average E. coli survival percentage on pure ZnO, ZnO/PDA, HAp@ZnO/PDA-06, HAp@ZnO/PDA-12, and HAp@ZnO/PDA-24 NPs at the concentration range from 200 to 6.25 µg/mL was around 52%, 59%, 59%, 57%, and 55% respectively while the average S. aureus survival percentage on those NPs at the concentration range from 200 µ to 6.25 µg/mL was around 37%, 45%, 47%, 45%, and 41% respectively. In terms of cytocompatibility, the HAp@ZnO/PDA NPs treated samples showed enhanced MC3T3-E1 cell adhesion and proliferation when compared to pure ZnO NPs. The result explained that in all the tested NPs above 50 µg/mL, the cell viability is less than 50% while the concentration of NPs below 50 µg/mL showed more than 100% of cell viability, and at 50 µg/mL, the cell viability exhibited by pure ZnO, ZnO/PDA, HAp@ZnO/PDA-06, HAp@ZnO/PDA-12, and HAp@ZnO/PDA-24 composite NPs was 42%, 75%, 83%, 78%, and 70% respectively in average. Moreover, the cell viability reached above 350% in the 6.25 µg/mL of NPs treated samples. Hence, the study concluded that preparing HAp@ZnO/PDA composite NPs following mussel-inspired PDA coating and simulated body fluid (SBF) incubation techniques provided a facile way for the enhancement of the cytocompatibility of ZnO NPs without losing its potential antibacterial properties.

Specific microorganisms in the human gut (i.e., gut microbes) provide mutually beneficial outcomes such as microbial balance by inhibiting the growth of pathogenic organisms, immune system modulation, fermentation of ingested products, and vitamin production. The intake of contaminants including potenially toxic elements (PTEs) can occur through food, air, water and some medicines. The gut microbes not only can be affected by environmental contaminants but they themselves can alter the speciation and bioavailability of these contaminants. This research work was designed to demonstrate the relationship between increasing level of selected PTEs including As, Cd, Pb and Hg on the growth of selected gut microbes. The toxicity of above mentioned PTEs to three gut bacteria (Lactobacillus rhamnosus, Lactobacillus acidophilus and Escherichia coli) was examined. While the toxicity of all the cationic PTEs including Cd, Pb and Hg towards gut bacteria decreased with increasing pH, the anionic As species exhibited an opposite effect. The order of toxicity was Hg > Cd > Pb > As(III)>As(V) for E. coli; and Hg > Cd > As(III)>Pb > As(V) for the two Lactobacillus sp. Arsenite (AsIII) showed higher toxicity than arsenate (AsV) to gut bacteria. While As is an anion, Cd, Pb and Hg are cations and hence their binding capacity to the bacterial cell wall varied based on the charge dependent functional groups. However, the toxic effects of PTEs for a bacteria are controlled by their speciation and bioavailability.

Maitake polysaccharides, after hydrothermal processing, were fermented with Lactobacillus acidophilus CCFM202 (L.A.) and Lactobacillus plantarum CCFM6392 (L.P.). The degradation of molecular weight of polysaccharides by hydrothermal processing under acidic conditions was obviously enhanced, which turned part of the water-insoluble-polysaccharides (WIP) into water-soluble-polysaccharides (WSPs). The pH value of water-soluble-polysaccharides (WSPs) and water-insoluble-polysaccharides (WIPs) were intensely dropped (4– 5) after 24 h fermentation. The optical density (O.D.) was increased (1.4– 2.3) due to bacterial growth, and short-chain fatty acids also followed this trend. LA-WSP predominantly produced acetic acid, 3– 4 folds to lactic acid, while LP-WIP groups produced dominant butyric acid (15– 17 folds). Hydrothermal processing induced the growth of L.A. and L.P., where the highest abundance was 2.5 × 10⁴. From the Venn diagram, WSP-1 produced the most elevated metabolites (874). Therefore, experimental results show a significant impact on making WSPs fragments, whereas temperature and pH influence the WSPs degradation, withstand to higher fermentation efficacy.